Having trailed in polls of the Midwestern bellwether all year, the Republican candidates were touring the state urging voters in its conservative rural counties to help them grow a “bountiful harvest of new jobs”.

“America is more than just a piece of geography,” Mr Ryan told hundreds of farmers at a remote school in Sabina.

“It is more than our corn fields, our bean fields and our dairy farms. It is an idea.”

At a rally in Celina, Mr Romney last night promised: “We know where we want to lead the country to get America strong again,” prompting ear-splitting chants of “USA!” by thousands of supporters.

Aiming to sway undecided moderates viewing the event in television bulletins, he also boasted that “independent voters and some Democrats” were flocking to his campaign.

The former Massachusetts governor is aiming to replicate the success in 2004 of George W Bush, who won a shock victory in Ohio — and re-election — by sharply boosting rural turnout.

The state has backed the winning presidential candidate in every election since 1964, and is poised yet again to be the “tipping point” that signals which man has triumphed in the Electoral College.

Mr Obama now leads polls of Ohio by an average of just 1.9 per cent, down from 5.5 before his defeat in the first presidential debate on Oct 3.

While Mr Romney holds an average national lead of 0.9 per cent, Republicans concede Ohio is critical.

Nicolle Wallace, a former aide to Mr Bush, told ABC News yesterday: “I don’t buy that there’s a path without Ohio for Romney.”

He will easily win areas such as Celina and Sabina, small and old-fashioned towns between vast expanses of stubbled corn and sheep fields, which backed John McCain over Mr Obama in 2008 by 30 points.

Introducing Mr Ryan in Sabina, the local State Representative Cliff Rosenberger compared the country’s dire economic situation to the severe drought during this year’s blistering summer.

“Our crops withered and died in the field,” said Mr Rosenberger. “It was painful to watch.”

But just as a “refreshing rain” eventually came, he said, “Romney and Ryan can be the simple change in the weather we need to end this economic drought”.

“Ryan is one of us,” said Jay Laycock, a 65-year-old farmer. “Obama scares me.”

However, to win the state, Mr Romney will also need to rack up more challenging victories from six “swing counties” that switched to Mr Obama four years ago after supporting Mr Bush in 2004.

While Mr Obama campaigns in Ohio today with Bill Clinton, and returns for solo stints across the state on Wednesday and Friday, Mr Romney will continue campaigning here today and tomorrow before returning with Mr Ryan for a large rally on Friday.

“It’s going to be tight,” said Ben Kimmel, a Romney campaign volunteer. “He has got to win Ohio. His people are saying there’s a way without it, but I just don’t see it.”

With one in eight jobs in Ohio linked to the automotive industry, Mr Obama’s stubborn lead here is attributed to his bail-out of America’s carmakers, which Mr Romney opposed.

Mr Ryan, however, attacked the President for “picking losers as well as winners” in the bail-out, which led to some local workers for a former branch of General Motors losing their pensions.

“We got nothing,” said Frank Parks, 63, one such worker and the only black supporter at the event. He added: “Black folks say Republicans are racist, but they’re the ones voting for a guy just because he’s black.”

Mr Knecht, 49, warned that Mr Obama would suffer from anger at the loss of 8,000 jobs in the area due to the departure of DHL, the shipping firm — a decision made before he was elected, but enacted afterwards.

“But considering the Republicans in Congress have tried to block him at every turn,” said Mr Knecht. “Obama has done the best he could.”